Smoke billows from buildings following an Israeli air strike in Gaza City on July 11, 2014. (AFP)

An airstrike outside a family home early Saturday pushed the Palestinian death toll past 100 in four days of cross-border fighting as Israel showed no sign of pausing despite international pressure to negotiate a ceasefire with the militants.

Asked if Israel might move from the mostly aerial attacks of the past four days into a ground war in Gaza to stop militant rocket fire, Prime Minister Benjamin Netanyahu replied, "We are weighing all possibilities and preparing for all possibilities."

"No international pressure will prevent us from acting with all power," he told reporters in Tel Aviv a day after a telephone conversation with US President Barack Obama about the worst flare-up in Israeli-Palestinian violence in almost two years.

Today, Washington affirmed Israel's right to defend itself in a statement from the Pentagon. But Defence Secretary Chuck Hagel told Israeli Defence Minister Moshe Ya'alon he was concerned "about the risk of further escalation and emphasized the need for all sides to do everything they can to protect civilian lives and restore calm."

An Israeli airstrike killed five youths and wounded 15 people outside a family home in the Jabalya refugee camp in the northern Gaza Strip early on Saturday, witnesses and medical officials told reporters.

A rocket seriously wounded one person and injured another seven Israelis when a fuel tanker was hit at a service station in Ashdod, 30 km (20 miles) north of Gaza. Palestinian militants warned international airlines they would fire rockets at Tel Aviv's main airport.

Medical officials in Gaza said at least 75 civilians, including 23 children, were among 106 people killed in the aerial bombardments that Israel began on Tuesday. They included 12 killed today.

Among the dead was a man described by Palestinian officials as a doctor and pharmacist. A 4-year-old boy was killed when a neighbour's house was targeted by an Israeli raid, a Palestinian hospital official said. Two other people aged 70 and 80 were killed in a missile strike elsewhere in Gaza, the Palestinian Heath Ministry said.

Fire was also exchanged across Israel's northern border. Lebanese security sources said two rockets were fired into northern Israel today but they did not know who had fired them. Israel responded with artillery fire. Palestinian groups in Lebanon have often fired rockets into Israel in the past.

Lebanese security forces arrested a Lebanese man suspected of firing the rockets with two Palestinians, the national news agency said. The Israeli military said they caused no damage.

Palestinians said Israeli tanks fired shells east of Rafah, ships shelled a security compound in the city of Gaza and aircraft bombed positions near the Egyptian and Israeli borders.